Solar collectors are well known in the field of generating and storing energy. Solar collectors typically take a working fluid and channel it through heat exchangers that are exposed to solar radiation and have a high surface area to volume ratio. Such solar collectors may be either flat sheets or include one or more pipes through which a working fluid flows while absorbing heat from solar radiation. Such a solar energy heat exchanger may be used in conjunction with apparatus for the concentration of solar energy such as lenses and curved mirrors. U.S. Pat. No. 4,078,549 issued Mar. 14, 1978, to McKeen, et al., and entitled "Solar Energy Collector", illustrates the use of a parabolic reflector mirror to focus solar radiation through substantially a single linear focal point. The patent discloses a single heat exchanger tube positioned at the focal point for receiving the focused radiant energy. This patent further discloses tracking apparatus for pivotally moving the reflective surface of the collector to maintain it in alignment with the position of the sun during normal daylight hours.
U.S. Pat. No. 3,708,979, issued Jan. 9, 1973, to Bush, et al., and entitled "Circuital Flow Hot Gas Engines", teaches the use of a two-stage heat exchanger in the context of a hot gas engine wherein the working fluid is pre-heated in an interchanger stage by the exhaust of the engine and then is further heated in a second, heater, stage which consists of a fuel-burning furnace, as is known in the art. The patent further teaches the use of a compressor comprised of a first piston and cylinder assembly and an expander comprised of a second piston and cylinder assembly having a larger diameter than the compressor. The pistons of the expander and compressor are interconnected so that they move in unison and the expander has a predetermined cross-sectional area relative to the compressor such that a stroke of the expander piston removes the same mass of heated working fluid from the heat exchanger as was introduced to the heat exchanger by one stroke of the compressor.
U.S. Pat. No. 4,094,146 issued to Schweitzer on June 13, 1978, discloses a single piston combined compressor and expander for use with a solar collector wherein a single diameter piston has two functional faces, one face functionally operating as an expander and the opposite face functionally operating as a concurrent compressor.
It is also generally known in the art to utilize a crank shaft or other mechanical linkage to cause multiple piston assemblies to operate in a coordinated manner such that the compression stroke of one piston may be powered by the expansion stroke of another.
Each of these known prior designs has certain limitations, for example, low efficiency, requirement of a closed system, numerous moving parts, difficult or expensive manufacture of parts, high costs, and low power outputs.
It is accordingly an object of the present invention to disclose and provide a solar engine that operates on an open cycle using air as the working fluid, the air exhibiting the well known thermodynamic properties of an air-standard cycle, where air is withdrawn from and returned to the atmosphere.
It is another object of the present invention to simplify and reduce the number of moving parts and linkages in a hot air solar engine piston assembly.
It is a further object of the present invention to disclose and provide a hot air solar engine having an engine portion which is substantially symmetric and easy to manufacture.
It is yet a further object of the present invention to provide a second, auxilliary heat source for a hot air solar engine thereby allowing 24-hour operation, as well as providing a combined solar and auxilliary heat source operation which produces an increased power level.
It is still a further object of the present invention to increase the energy efficiency of a hot air solar engine by recovering heat from its exhaust.